Grid welding machines of this type are already known for various uses, for example in order to be able to attach, by welding, transverse wires of the desired length of sections, corresponding to wire mats of a group assembly or bunch of longitudinal wires. The transverse wires are fed alternately on the top and the underside of the longitudinal wire bunch, so that it becomes possible to stack, in a space-saving manner, the grid mats cut into sections, without turning them by 90.degree., by engagement of the transverse wires of one mat into the spaces between the transverse wires of the neighboring mat (see, for example, Austrian Patent AT-PS 215.268). In another manner of application, the transverse wires brought in above and below the longitudinal wire bunch are selectively welded together with associated wires of a longitudinal wire bunch in such a way, that two grid bodies are created simultaneously, the longitudinal wires of the one grid body lying in the spaces between the longitudinal wires of the other grid body (see German Patent Disclosure Document DE-OS 26 22 167).
It is an present invention to design a grid welding machine of the species recited above in such a way that it allows, in a simple and operational safe way, the production of welded grids in which two transverse wires group or are located opposite each other in a longitudinal wire bunch in order to stiffen the grid in this way and when the grid is used for reinforcement of concrete, to improve the anchoring of the reinforcement grid in the concrete.
Briefly, in accordance with the invention, during an operating cycle, first two rows of electrodes are movable, up- or downwardly, respectively, away from the longitudinal wire path in order to allow the simultaneous supply of wires of the wire bunch. Two transverse wires are then simultaneously transported into the weld positions between the two rows of electrodes. The transverse wires are placed against the longitudinal wires of the wire bunch, located between the transverse wires. One row of electrodes can be immobilized and backed up, so that the electrodes of the one row form abutment, or counter, or back-up supports, while welding pressure can be applied to the electrodes of the other row, so welding pressure can be applied to the other row of electrodes, so that each longitudinal wire is simultaneously welded together with the two abutting transverse wires by means of the welding current flowing between each pair of electrodes in series via the intersecting point between one longitudinal wire and two abutting transverse wires.
In a preferred embodiment of the invention, wherein the electrodes of the two rows have been mechanically combined in pairs into a unit by means of a connecting piece extending through the longitudinal wire path, flexible copper braids are inserted in the power supplies of the two electrodes.
In accordance with a feature of the invention the electrodes of the one row are attached to a common electrode bar which can, during the work cycle, be mechanically displaced in relation to the longitudinal wire path, for example by an eccentric or a cam drive, into a rigid abutment position; hydraulic cylinders are assigned to the electrodes of the other row, which can also displaced in relation to the longitudinal wire path and charged with welding pressure.
In accordance with another feature of the invention, the transverse wire feeder for the upper transverse wires brings each transverse wire into the weld position by means of gravity, while the transverse wire feeder for the lower transverse wires has fork-like feed elements which, by means of the fork, each take up a lower transverse wire and lift it into the weld position along a prescribed feed path.
Further characteristics of the invention ensue from the following description of an exemplary embodiment by means of the drawings.